|You don't need the disc.|
Connect to the router to a computer via cable.. Set you computer to obtain IP address automatically. Reboot. Go to a Command prompt and type configure /all. Enter the IP address for Default Gateway into your web browser. The default is 192.168.1.1 but this could have changed. That will put you the routers configuration interface. From then on just follow the manual.
You may get prompted for a user name and password. The default for Linksys is blank for user-name and admin for password. If this doesn't work ask your Aunt what it has been set to. If she cannot remember you are going to have to reset to factor defaults. To do this press the reset button at the back of the router and hold for five seconds. You will need power applied to do this and a straightened paper clip or something similar to push through the reset hole.